1. Field of the Invention
The present invention relates to a position detection apparatus for detecting a position of movement of two members which move relative to each other.
2. Description of the Related Art
Heretofore, a position detection apparatus for detecting a position of movement of two members which move relative to each other is well known. This position detection apparatus comprises a scale on which a periodic signal whose signal level varies in a certain wavelength is recorded along a certain direction, a head section for detecting the periodic signal recorded on the scale, and an arithmetic processing section for performing signal processing of the periodic signal detected by the head section to output position information. The scale and the head section are fitted to a moving element and a base element of two members moving relative to each other. The position detection apparatus detects with the scale the periodic signal whose signal level changes, and supplies the detected periodic signal to the arithmetic processing section. The arithmetic processing section outputs position information showing a position of relative movement of the two members, based on the periodic signal detected by the head section.
The position detection apparatus generally outputs a two-phase increase and decrease pulse, a so-called A/B phase signal, as position information. The two-phase increase and decrease pulse is composed of two signals, A phase signal and B phase signal, which have the same period to each other and whose phases are shifted by xc2xc period. The two-phase increase and decrease pulse is a signal showing a Gray coded two-bit count value, with the A phase signal designated as a lower bit, and the B phase signal designated as an upper bit. This count value shows a quantity of relative movement. In this manner, if the two-phase increase and decrease pulse is transmitted as position information, the quantity of information to be transmitted can be reduced. Moreover, since the displacement is shown using the Gray code, the direction of movement can also be transmitted clearly. Then, a control unit or the like which obtains the two-phase increase and decrease pulse from the position detection apparatus 1 as position information cumulatively adds (subtracts when two members move in the negative direction) the number of count of the two-phase increase and decrease pulse, to thereby determine the quantity of relative movement of two members, thereby controls a position of movement of two members.
Moreover, an origin signal showing an origin of the relative movement position is recorded on the scale together with the periodic signal. The position detection apparatus outputs a reference origin pulse, when the head section detects the origin signal recorded on the scale. A control unit or the like which has obtained the reference origin pulse starts counting the two-phase increase and decrease pulse from the time when the reference origin pulse is output.
With the position detection apparatus, one wavelength of the periodic signal recorded on the scale is further divided, to thereby detect a movement position of two members which move relative to each other. For example, one wavelength is divided into 40, 100, 360, 1000 or the like to perform position detection.
With a conventional position detection apparatus, when one wavelength of the periodic signal is further divided in such a manner, the two-phase increase and decrease pulse to be output is generated, using a conversion table wherein angle data obtained by performing polar conversion with respect to the periodic signal and signal level data of the periodic signal are designated as an address. However, the size of the conversion table is very large to correspond to many kinds of the number of divisions, causing cost increase. Moreover, quantize error occurs due to the conversion table, resulting in deterioration in the precision.
Furthermore, with the position detection apparatus, the two-phase increase and decrease pulse for outputting the position information divided by a predetermined number of divisions must be output synchronously with the origin signal.
It is an object of the present invention to provide a position detection apparatus which can divide one wavelength of a periodic signal recorded on a recording medium by an optional number of divisions and calculate and output a two-phase increase and decrease pulse which increases or decreases depending on the movement per unit of number of divisions with a small quantity of arithmetic operation.
Moreover, it is an object of the present invention to provide a position detection apparatus which can output a reference origin pulse synchronized with the two-phase increase and decrease pulse, as well as calculating and outputting the two-phase increase and decrease pulse with a small quantity of arithmetic operation.
To solve the above-described problems, the position detection apparatus according to the present invention comprises: a recording medium on which a position signal comprising a periodic signal is recorded; a detection section comprising a first detection head which moves relative to the recording medium along the recording direction of the position signal for detecting the position signal, and a second detection head which is disposed apart from the first detection head by a predetermined distance in the recording direction of the position signal, and moves relative to the recording medium, operating together with the first detection head for detecting the position signal; a polar conversion section for converting the position signal detected by the first detection head and the second detection head into 2-bit quadrant signal showing a relative position of the recording medium and the detection section in a unit of quadrant in one period of the position signal, and an in-quadrant angle signal showing a relative position of the recording medium and the detection section as an angle in each quadrant; and an output section for outputting a two-phase increase and decrease pulse, based on the quadrant signal, the in-quadrant angle signal and a number of divisions signal showing a number of divisions in the quadrant of the position signal, such that one pulse is generated when the recording medium and the detection section move relative to each other for a distance obtained by dividing one quadrant of the position signal by the number of divisions.
The output section of this position detection apparatus comprises: a first multiplier for multiplying the in-quadrant angle signal and the number of divisions signal, and extracting a bit number same as the number of divisions signal from the upper bit of the multiplication result to thereby generate an in-quadrant division address signal; a second multiplier for multiplying lower 2 bits of the number of divisions signal and the quadrant signal; an adder for adding lower 2 bits of the in-quadrant division address signal output from the first multiplier and lower 2 bits in the multiplication result of the second multiplier; and an increase and decrease pulse generator for generating the two-phase increase and decrease pulse by encoding the lower 2 bits in the multiplication result of the adder.
With this position detection apparatus, the in-quadrant angle signal and the number of divisions signal are multiplied, and the upper bit is extracted to generate an in-quadrant division address signal, then the lower 2 bits from the multiplication result of multiplying lower 2 bits of the number of divisions signal and the quadrant signal, and lower 2 bits of the in-quadrant division address signal are added, to generate a two-phase increase and decrease pulse based on the lower 2 bits in the added result.
Moreover, the position detection apparatus according to the present invention comprises: a recording medium on which a position signal comprising a periodic signal and an origin signal showing an origin position of the position signal are recorded; a detection section comprising a first detection head which moves relative to the recording medium along the recording direction of the position signal for detecting the position signal, a second detection head which is disposed apart from the first detection head by a predetermined distance in the recording direction of the position signal, and moves relative to the recording medium, operating together with the first detection head for detecting the position signal, and a third detection head which moves relative to the recording medium, operating together with the first detection head for detecting the origin signal; a polar conversion section for converting the position signal detected by the first detection head and the second detection head into 2-bit quadrant signal showing a relative position of the recording medium and the detection section in a unit of quadrant in one period of the position signal, and an in-quadrant angle signal showing a relative position of the recording medium and the detection section as an angle in each quadrant; and an output section for outputting a two-phase increase and decrease pulse, based on the quadrant signal, the in-quadrant angle signal, the origin signal detected by the third detection head and a number of divisions signal showing a number of divisions in the quadrant of the position signal, such that one pulse is generated when the recording medium and the detection section move relative to each other for a distance obtained by dividing one quadrant of the position signal by the number of divisions, and a reference origin pulse generated when the position of relative movement of the recording medium and the detection section is the origin position.
The output section of the position detection apparatus comprises: a first multiplier for multiplying the in-quadrant angle signal and the number of divisions signal, and extracting a bit number same as the number of divisions signal from the upper bit in the multiplication result to thereby generate an in-quadrant division address signal; a second multiplier for multiplying lower 2 bits of the number of divisions signal and the quadrant signal; an adder for adding lower 2 bits of the in-quadrant division address signal output from the first multiplier and lower 2 bits in the multiplication result of the second multiplier; an increase and decrease pulse generator for generating the two-phase increase and decrease pulse by encoding the lower 2 bits in the multiplication result of the adder; an in-quadrant reference address generator for generating an in-quadrant reference address signal, when a signal excluding the lower 2 bits of the in-quadrant division address signal is a predetermined signal; and an origin signal generator for generating the reference origin pulse, when the origin signal is detected by the third detection head, the quadrant signal is a predetermined quadrant, the in-quadrant reference address signal is generated, and the two-phase increase and decrease pulse is a predetermined phase.
With this position detection apparatus, the in-quadrant angle signal and the number of divisions signal are multiplied, and the upper bit is extracted to generate an in-quadrant division address signal, then the lower 2 bits from the multiplication result of multiplying lower 2 bits of the number of divisions signal and the quadrant signal, and lower 2 bits of the in-quadrant division address signal are added, to generate a two-phase increase and decrease pulse based on the lower 2 bits in the added result. Moreover, with this position detection apparatus, when a signal excluding the lower 2 bits of the in-quadrant division address signal is a predetermined signal, the in-quadrant reference address signal is generated, and the reference origin pulse is generated, when the origin signal is detected by the third detection head, the quadrant signal is a predetermined quadrant, the in-quadrant reference address signal is generated, and the two-phase increase and decrease pulse is a predetermined phase.
With the position detection apparatus according to the present invention, the in-quadrant angle signal and the number of divisions signal are multiplied, and the upper bit is extracted to generate an in-quadrant division address signal, then the lower 2 bits from the multiplication result of multiplying lower 2 bits of the number of divisions signal and the quadrant signal, and lower 2 bits of the in-quadrant division address signal are added, to generate a two-phase increase and decrease pulse based on the lower 2 bits in the added result.
Thereby, with this position detection apparatus, the two-phase increase and decrease pulse which increases or decreases in a unit obtained by dividing one wavelength of the position signal recorded on a recording medium by an optional number of divisions can be calculated with a small quantity of arithmetic operation and output.
Furthermore, with the position detection apparatus according to the present invention, the in-quadrant angle signal and the number of divisions signal are multiplied, and the upper bit is extracted to generate an in-quadrant division address signal, then the lower 2 bits from the multiplication result of multiplying lower 2 bits of the number of divisions signal and the quadrant signal, and lower 2 bits of the in-quadrant division address signal are added, to generate a two-phase increase and decrease pulse based on the lower 2 bits in the added result. Moreover, with this position detection apparatus, when a signal excluding the lower 2 bits of the in-quadrant division address signal is a predetermined signal, the in-quadrant reference address signal is generated, and the reference origin pulse is generated, when the origin signal is detected by the third detection head, the quadrant signal is a predetermined quadrant, the in-quadrant reference address signal is generated, and the two-phase increase and decrease pulse is a predetermined phase.
Thereby, with this position detection apparatus, the two-phase increase and decrease pulse which increases or decreases in a unit obtained by dividing one wavelength of the position signal recorded on a recording medium by an optional number of divisions can be calculated with a small quantity of arithmetic operation and output. Moreover, with this position detection apparatus, the reference origin pulse synchronized with the two-phase increase and decrease signal can be output at a predetermined one place on the recording medium.